Shikai2070

I have a old french mercier cruiser that has cotterted cranks, unfortunately the drive side crank arm is bent and needs to be replaced. I have another set of cranks from another vintage road bike that i would like to replace with but these were secured into the other bike with different sized cotter pins. Will they work on the cruiser if i use the same size pins that were originally on the cruiser or are the pins crank specific aswell?

merziac

Maybe, the axle/spindle has to be the same size as the crank arms and yes the pins may have to be the same but are often hand filed to fit correctly.

So you need a good basic understanding, compatible parts and likely some finesse through trial and error.

gaucho777 

Cotter pins are not always interchangeable.

Quoting the esteemed Sheldon Brown: "Replacement cotters that fit well are not always easy to find. There is very limited interchangeability. The diameter of the round part of the cotter tends to be standardized according to nationality. Most use 9.5 mm, including British, Asian and most German bicycles. French and Italian bicycles used 9 mm, or sometimes 8.5 mm."

https://www.sheldonbrown.com/cotters.html

jackbombay

How bent is the bad crank? It could likely be straightened and used indefinitely, no compatibility/cotter pin issues if you do that...

Shikai2070

i tried with two wrenches but it wouldnt budge. Seems like its really hard steel. Any tips?

jackbombay

Blocks of wood and a large hammer! Or blocks of wood and a bench vice and a large hammer! but always have a piece of wood between the crank and the hammer so you don't break the chrome!

If you really can't get it to move I'd be glad to give it a shot if you mail it to me,%99 of the time I fix things, %1 of the time I mess them up so bad they will never work correctly again :-P

Shikai2070

im in canada so postage might be too much. What do you mean by a couple blocks of wood and a big hammer? If you could explain more!

jackbombay

Hard to say without knowing how the crank is bent, but if its just bent a bit I would start by taking the pedal off the crank with the crank on the bottom bracket spindle and place a pipe over the crank arm and try to bend it straight like that, if its really bent I'd start by taking the crank off the bike and supporting it with blocks of wood and hitting it with a hammer to get it close to straight then reinstall it to get it straight by removing the pedal and sliding a pipe over the end of the crank arm and bending it straight.

A pipe placed over the end of the crank arm really should be able to bend the crank, something hit the crank before that bent it, there is no reason that same amount of force can't be applied in the opposite direction to correct the issue.

Shikai2070

il give it a shot!

merziac

Look up BFH for an idea, blocks, vice, finesse and force carefully applied in the correct manner can yield results if you can do it right.

RJ the bike guy may have a youtube video but again, this takes a good basic understanding of the process and usually some practice to get there.

bikemig 

You could also think about running a cotterless crank. I fixed up a 1970s Peugeot UE 8 like that. I used the existing cups from the cottered crank but replaced the spindle with a cotterless one. I read somewhere that this could work and it did in my case (I think Sheldon Brown has something on this). The bearings hit the right spot on the spindle and it turns nicely.

SJX426 

I bought a used Tern D8 with a bent something because the pedal was not cycling through staying in the same orientation. Bent peddle? No, bent crank arm.

The doorway between the 2 car garage and the 1 car garage has exposed concrete foundation. The other hobby is Jeep XJ and 4x4 stuff. Naturally there is a high lift jack to support that off road event.

Two blocks of wood at either end of the crank to compensate for the off set were used on one foundation and the high lift was used against the other. Crank just past where it should be and done. Straight enough that it is not noticeable.

There was nothing to lose. If it broke, a new one would be required. If it deformed back to original, win.

WGB 

Shikai2070. Perhaps someone has an arm you can use. Post on the wanted/trades sticky. A photo would be useful

Most bike stores do not carry cotters anymore (st least not Canadian ones I've been to but most major cities have Co-ops. Ex. Hamilton has New Hope. I was there yesterday and they had junked an old Supercycle road bike frame with a cottered crankset. I recall debating taking the frame just for the Huret rear derailleur. You'll need either the original cotter or crank arm wirh you.

John E

Been there ... done that. The main issue seems to be thin-wall vs. thick-wall cups, particularly on the drive side. The only benefit of French or Italian threading is that one can use an adjustable cup on both sides, to provide a bit of fine-tuning in the driveline alignment. Otherwise, be sure to use thread locker on the so-called fixed cup, because they like to self-loosen on French and Italian bikes.

bikemig 

This is a good source for cotter pins:

Bicycle Crank Cotters

branko_76 

There are different diameters of cotter pins. My French Peugeot has 9mm pins and my English Raleigh has 9.5mm pins. You also need a safe method of removing the cotter pins. I used to use a hammer, block of wood, etc. and have destroyed the original pins. The best way to get them out without damaging anything is to use a cotter pin press like this...

New Crank Cotter Press

randyjawa 

Two issues might or will present themselves. The first is getting the correct size cotters. The second is spindle size. To fit these French cranks to an Italian spindle, for an old Torpado, I had to sand and sand and sand the Italian spindle a bit, both ends, to get it to fit into the crank. I had no issue with using the Italian cotters, as I recall...